In conventional portable communication terminals, such as a cell phone or personal digital assistant (PDA), the user interface typically includes an LCD display, a keypad for entering characters or a function to be performed by the terminal, and a scroll wheel or other similar pointing device enabling the user to, for example, highlight and select a particular item displayed on the display. Since there is a limited amount of surface area on the terminal, there is an inevitable tradeoff between the size of the terminal and the flexibility and functionality of the user interface.
Touch sensitive displays have been proposed as replacements for the keypad and pointing device. Instead of pressing keys on the keypads to enter characters and functions and using the pointing device to select displayed items, a user can enter characters and functions by touching objects displayed on the touch sensitive display. The touching may consist of taps, in which a point on the touch sensitive display is contacted and then the contact is released at the same point, or slides, in which the touch sensitive display is contacted at a first point and the contact moves to a second point where it is released.
While a touch sensitive display may render a separate keypad moot, there are still some considerations that should be taken into account when using a touch sensitive display on a portable communication terminal. Portable communication terminals are often small and it may be difficult to reliably touch the objects displayed on the touch screen. Entering information and functions via the touch screen is tedious in a moving vehicle, for example, since the accuracy of the contact suffers if the hand or stylus is unsteady. The slippery surface of the stylus tip also can complicate the contact with the desired areas on a touch screen. When touching an area on a touch screen with a stylus, for example, the stylus may slide an unintended distance from the first contact point before it is released. If the point of release of the contact happens to be in a different contact area than the one the touch originally was directed to, the character or function entered may not be the intended character or function or the contact may not be understood and will have to be repeated. This can be overcome by using a large touch screen but that adversely affects the size of the terminal. The size of the contact areas can be increased, but then a smaller number of areas can be displayed on the touch screen at the same time.
Additional user interface considerations also are created if the portable communication terminal utilizing a touch screen is capable of executing various multimedia applications, involving video, audio, imaging or Internet content. The conventional user interfaces for portable communication terminals are not the best match for multimedia terminals having touch screens.